used as a mild oath, expressing surprise US,1927 Popularised by baseball radio announcers Harry Caray and Phil Rizzuto.
“And then and there he assaulted the widow four times, you should excuse the expression.” “Holy cow!” whistled Nebbice. “Four times!” — Max Shulman, TheZebraDerby, p. 79, 1946
James McParlan II. Junior. James McParlan. Holy Cow. — Clancy Sigal, GoingAway, p. 179, 1961